STUDIES IN THE SIERRA* 

 By John Muir 



No. II. Mountain Sculpture, Origin of Yosemite Valleys 

 All the valleys and canons of the western flank of the Sierra, 

 between 36° and 39° north latitude, naturally classify them- 

 selves under two genera, each containing two species. One ge- 

 nus comprehends all the slate valleys, the other all that are built 

 of granite. The latter is far the more important, both on ac- 

 count of the greater extent of its geographical range and the 

 grandeur and simplicity of its phenomena. All the valleys of 

 both genera are valleys of erosion. Their chief distinguishing 

 characteristics may be seen in the following descriptions : 



Slate Valleys 



1. Cross-sections, V-shaped, or somewhat rounded at bottom, 

 walls irregular in structure, shattered and weak in appearance, 

 because of the development of slaty cleavage planes and joints, 

 which also prevent the formation of plane-faced precipices. Bot- 

 tom showing the naked bed-rock, or covered by rocky debris, 

 and sloping in the direction of the trend. Nearly all of the foot- 

 hill valleys belong to this species. Some of the older specimens 

 are smoothly covered with soil, but meadows and lakes are al- 

 ways zmnting. 



2. More or less widened, branching at the head. Bottom, with 

 meadows, or groves, or lakelets, or all together. Sections and 

 walls about as in No. i. Fine examples of this species occur on 

 the head-waters of the San Joaquin. 



Granite Valleys 

 I. Cross-sections narrowly or widely V-shaped. Walls seldom 

 interrupted by side canons, magnificently simple in structure 

 and general surface character, and presenting plane precipices 

 in great abundance. Bottom sloping in the direction of the trend, 



* Reprinted from the Overland Monthly of June, 1874. This is the second of a 

 series of seven studies in which Mr. Muir developed his theories of the geology of 

 the Sierra. — Editor. 



